1. Field of the Invention
The invention pertains to plant growth regulators and processes for their use. Plant growth regulators are substances which are used to influence the growth characteristics of plants. The growth characteristics influenced include growth rate, number of tillers produced per plant, standability of the plant, root stimulation and germination enhancement.
The plant growth regulators of the present invention are comprised of chitosan, which is a derivative of chitin. Chitin is a polysaccharide consisting predominantly, if not entirely, of unbroken chains of .beta.-(1-4)-linked 2-acetamido-2-deoxy-D-glucose (N-acetyl-D-glucosamine) residues. It can thus be regarded as a derivative of cellulose, in which the C-2 hydroxyl groups have been replaced by acetamido residues.
Chitin is found in huge quantities in the natural environment. Estimates of yearly production exceed several billions of tons. It is the structural material of all exoskeletal animals; of all members of arthropoda (crustacea, insects, spiders, etc.), mollusca (snails, squids, etc.), coelenterata (marine organisms such as hydoids and jellyfish) and nematoda (unsegmented worms). Chitin is also found in various fungi.
In crustacea, the shell comprises a matrix of protein chemically combined with chitin which is mixed with calcium carbonate. In order to free the chitin from the protein, the shell of the crustacean is treated with an alkaline aqueous solution which penetrates the interstices of the shell matrix to rupture the bond between the protein and chitin. To then separate the chitin from the calcium carbonate, the residue from the protein separation is treated with an acid to remove the calcium carbonate and leave substantially pure chitin. The acid used is preferably hydrochloric acid.
The demineralized chitin is washed on a rotary vacuum filter and dried in a rotary hot-air dryer. At this point, the chitin can be converted directly to one of its derivatives, chitosan. Chitin is a less reactive compound than the related compound, cellulose, and because of this property, it has been little used by industry. Some uses include as a dry hair shampoo, a flocculent, and a matrix for photo processing and for some enzymes.
2. Description of the Prior Art
Chitin has also been used as an adhesive, as described by Rigby in U.S. Pat. No. 2,047,226, as a sizing agent for paper, as disclosed by Merrill in U.S. Pat. No. 2,047,218, as an emulsifier, as disclosed by Rigby in U.S. Pat. No. 2,047,225, and as filaments, threads, fibers, tubes, straws and seamless sausage casings, as disclosed by Thor in U.S. Pat. No. 2,217,823.
Muzzarelli, in Chitin, Pergamon Press (1977), at pages 207-254, has described industrial uses of chitin including the removal of certain radioisotopes from water by percolation, the removal of mercury and copper from water, as a textile finish, in polymeric dyes, as a soil repellant, as a shrinkproofing for wool, in photographic products and processes, and in dewatering municipal sludge. At pages 255-265, Muzzarelli describes medical uses of chitin including artificial kidney membranes, preparations for immunization against parasites, biodegradable -pharmaceutical carriers, blood anticoagulants, aggregation of leukemia cells, wound healing accelerators and microbiologic media.
Additionally, chitin has been used to form a gel for encapsulating somatic embryos, zygotic embryos or meristematic tissue of plants, as described by Redenbaugh in U.S. Pat. No. 4,562,663. The use by Redenbaugh of chitin as an encapsulating medium is unrelated to any plant growth regulation function. As explained by Redenbaugh, the encapsulation medium "must allow the meristem or embryo respiration by permitting diffusion of gases". The encapsulation medium should also "provide an environment strong enough to resist external abrasion and adverse forces, yet pliable enough to allow the growth of the embryo and its germination at the appropriate time".
Chitosan has also been used to reduce the lodging of wheat plants, as described by Hadwiger in the published Australian Patent Application No. 47960/85. The chitosan is dissolved in dilute acetic acid, and after further dilution with water, the chitosan solution is applied to wheat seeds. The wheat plants then show increased stem diameters and increased root development.
Use of chitin as plant fertilizer has been disclosed by Peniston et al. in U.S. Pat. No. 4,199,496. Although the Peniston et al. patent is concerned with processes for the recovery of chemicals from the shells of crustacea, the use of chitin as a fertilizer is mentioned because chitin is one of the chemicals recovered from the shells of crustacea. As explained by Peniston et al., chitin can be used as a fertilizer to release nitrogen, slowly, into the soil and thereby over a relatively long period of time increase the nitrogen content of the soil".
However, fertilizers differ from plant growth regulators. A fertilizer is any material which is added to soil to supply chemical elements needed for plant nutrition. Most commonly, fertilizers are designated by a three-digit number which represents the respective amounts of nitrogen, phosphorus and potassium. A plant growth regulator, on the other hand, is an organic compound which will inhibit, accelerate or in some way influence physiological processes in plants. Where a fertilizer merely supplies needed elements for a plant to grow in its normal fashion, a plant growth regulator causes some sort of change in the plant's normal growth pattern. Some of the influences of plant growth regulators include germination enhancement, root stimulation, plant stature control, shortening or lengthening of the time to maturity of the plant, ripening control, increased yield, fruit and vegetable color control, and shortened or lengthened dormancy. Some known plant growth regulators are cytokinins and gibberellic acids.
At present, there are no known materials which have the ability to influence, affect enhance or increase the reproductive sites, e.g., tillers, pods, ears, etc., of plants. There are also no known derivatives, compositions or combinations of chitin used as plant growth regulators.